We Live In a Toxic World – Part III: Examples of Chemicals Carcinogenic to Humans

We Live In a Toxic World – Part III: Examples of
Chemicals Carcinogenic to Humans

Michael Garko, Ph.D.
Host – Let’s Talk Nutrition

Introduction

According to the International Agency for Research on Cancer (IARC), it is generally accepted that “80% of all cancers are directly or indirectly linked to environmental factors, and, thus, are preventable” (International Agency for Research on Cancer, 2008a, p. 1).

An important part of the IARC’s (2008a) mission is to identify the causes of human cancer. The IARC (2008a) considers this to be the first step in cancer prevention. It is reported in its Preamble to IARC Monographs on the Evaluation of Carcinogenic Risks to Humans that “the global burden of cancer is high and continues to increase: the annual number of new cases was estimated at 10.1 million in 2000 and is expected to reach 15 million by 2020” (International Agency for Research on Cancer, 2006, p. 1).

The IARC (2008b; 2007b) classifies environmental factors (e.g., chemicals, complex mixtures, occupational exposures, physical & biological agents & lifestyle factors) which can increase the risk for cancer in humans into three groups: Group 1 – Carcinogenic to Humans, Group 2A – Probably Carcinogenic to Humans and Group 2B – Possibly Carcinogenic to Humans. To date, the IARC has identified 105 agents and groups of agents as Carcinogenic to Humans, 66 agents and groups of agents Probably Carcinogenic to Humans and 248 agents and groups of agents Possibly Carcinogenic to Humans for a total of 419 agents with some greater or lesser potential to cause cancer. It is important to point out that national health agencies in the United States use this information as scientific support for their actions to prevent exposure to potential carcinogens.

The September, 2008, issue of Healthful Hints, presents a discussion on two chemicals from IARC’s Group 1 known to be Carcinogenic to Humans. The two chemicals are asbestos and benzene. Both chemicals are reported to be pervasive in the environment and cause serious health issues, including cancer. Included in the discussion on asbestos and benzene is information on the uses, sources and potential exposure, assessing personal exposure and health hazards associated with the two chemicals.

While asbestos and benzene are just two examples of cancer causing agents found in the environment, they were selected because they are illustrative of the depth and breadth of what scientists and medical researchers know about the carcinogens pervading the environment. They were also selected because they can serve to give readers a sense of how dangerous it can be to live in toxic world constituted of carcinogenic agents. Readers are encouraged to visit the sources and related websites of the IARC, DHHS and EPA found in the Reference section at the end of the newsletter to learn more about those environmental factors associated with increasing the risk for cancer.

Asbestos

Based on the classification of carcinogenic agents by the IARC, asbestos is listed in its Group 1 category and evaluated as being “Carcinogenic to Humans” (see International Agency for Research on Cancer, 2007a).

According to the U.S. Department of Health and Human Services (2007), “Asbestos and all commercial forms of asbestos are known to be human carcinogens based on sufficient evidence of carcinogenicity in humans” (p. 1).

Asbestos is the generic name for six naturally occurring fibrous silicate minerals. They are chrysotile (a fibrous serpentine mineral) and actinolite, amosite, anthophyllite, crocidolite and tremolite (five fibrous amphibole minerals) (see U.S. Department of Health and Human Services, 2007).

Uses of Asbestos

The use of asbestos dates back as far as 2,000 years ago. However, the modern day industrial application of asbestos began around 1880 and peaked during the late 1960s and early 1970s at which time approximately 3,000 industrial applications or products were in use. The development of asbestos in the United States was created by the high demand for it from 1900 to the early 1970s. By the 1950s, the United States became the largest developer and user of asbestos. The high demand for asbestos dropped off rapidly after 1973 when its use became a significant health and liability issue (see U.S. Department of Health and Human Services, 2007).

Asbestos has been applied industrially in the making of roofing materials, thermal and electrical insulation, cement pipe and sheets as coverings, resins, plastics as reinforcement, flooring, gaskets, friction materials for brake linings and clutch facings, coatings and compounds, textiles, paper and other industrial products (see U.S. Department of Health and Human Services, 2007).

Sources and Potential Exposure

Humans become exposed to asbestos and its deleterious effects primarily through inhalation and ingestion from outdoor and indoor sources. Asbestos finds its way into the environment from natural and anthropogenic sources. Specifically, according to the Environmental Protection Agency (EPA) (2007a), asbestos can be released into the air from the erosion of natural deposits in asbestos-bearing rocks, asbestos-related industries and from the clutches and brakes of cars and trucks. Asbestos can also find its way into soil and water from the erosion of natural deposits in asbestos-bearing rocks, corroded asbestos-cement pipes and disintegrated asbestos roofing materials which find their way into sewer systems.

In terms of indoor air exposure, asbestos can be released from damaged or disintegrated building materials such as insulation, along with ceiling and floor tiles. “Typical concentrations in indoor air range from 1 to 200 nanograms per cubic meter (ng/m3) (0.000001 to 0.002 milligrams per cubic meter (mg/m3) (Environmental Protection Agency, 2007a).

Asbestos Exposure Limits

In its 11th Report on Carcinogens, the U.S. Department of Health and Human Services (2007b) provided the following information from the Occupational Safety and Health Administration (OSHA), the American Conference of Governmental Industrial Hygienists (ACGIH) and National Institute for Occupational Safety and Health (NIOSH) regarding some of the regulations and guidelines for asbestos exposure limits:

The EPA (2007a) points out that people can be tested for the presence of asbestos fibers in urine, feces or mucus. They can also have a chest X-ray performed. A chest X-ray can detect early signs of lung disease caused by asbestos. However, it cannot detect the asbestos fibers themselves (See EPA 2007a).

Health Hazard Information on Asbestos

According to the National Institute of Occupational Safety and Health (NIOSH) (2007), “all levels of asbestos exposure studied to date have demonstrated asbestos–related disease” and “there is no level of exposure below which clinical effects do not occur” (p. 25). Thus, it would be prudent to avoid exposure to asbestos whenever possible.

Acute effects. According to the EPA (2007), no studies exist on the acute (short-term) toxicity of asbestos in animals or humans.

Cancer risk. The EPA (2007a) recognizes asbestos to be a human carcinogen. According to the EPA (2007a), occupational studies show that asbestos exposure through inhalation can cause lung cancer, mesothelioma and gastrointestinal cancer. Smokers exposed to asbestos have a greater than additive risk of developing lung cancer. Epidemiological studies reveal an association between exposure to asbestos from drinking water and cancer of the esophagus, stomach and intestines (see Environmental Protection Agency, 2007a).

The EPA (2007a) provides the following information on the estimated risk for cancer due to exposure to asbestos at certain levels:

EPA uses mathematical models, based on human and animal studies, to estimate the probability of a person developing cancer from breathing air containing a specified concentration of a chemical. EPA calculated an inhalation unit risk estimate of 2.3 × 10-1 (fibers/cm3)-1. EPA estimates that, if an individual were to continuously breathe air containing asbestos at an average of 0.000004 fibers/cm3 over his or her entire lifetime, that person would theoretically have no more than a one-in-a-million increased chance of developing cancer as a direct result of breathing air containing this chemical. Similarly, EPA estimates that breathing air containing 0.00004 fibers/cm3 would result in not greater than a one-in-a-hundred thousand increased chance of developing cancer, and air containing 0.0004 fibers/cm3 would result in not greater than a one-in-ten-thousand increased chance of developing cancer (Environmental Protection Agency, 2007a, pp.2-3).

Benzene

Based on the classification of carcinogenic agents by the International Agency for Research on Cancer (IARC), benzene is listed in its Group 1 category and evaluated as being “Carcinogenic to Humans” (see International Agency for Research on Cancer, 2007b).

Benzene is a prevalent deleterious chemical found in the environment. It is released into the atmosphere from natural sources (e.g., forest fires & oil seeps) and industrial sources (e.g., emissions from burning coal and oil, fuel evaporations from gasoline service stations & exhaust of motor vehicles) (see U.S. Department of Health and Human Services, 2005). It found also found in drinking water and tobacco smoke.

Uses of Benzene

The commercial production of benzene from coal began around 1849 and from petroleum since 1941. In 1994 in the United States, it ranked 17th in chemical production volume (U.S. Department of Health and Human Services, 2005).

The chemical and pharmaceutical industries have developed a number of wide-ranging applications for benzene. It is used as a solvent for fats, waxes, resins, oils, inks, paints, plastics and rubber and as a medium to extract oils from seeds and nuts. Within the gas and oil industry, benzene is a constituent or additive in gasoline or motor fuel and is used as a starting material and intermediate in the making of chemicals and gasoline. It is naturally present in crude oil and is a by-product of oil refining. The amount of benzene in unleaded gasoline is about one to two percent by volume. Finally, benzene is used in photogravure printing and the manufacture of detergents, explosives, pharmaceuticals and dyestuffs (see Environmental Protection Agency, 2007b; U.S. Department of Health and Human Services, 2005).

Sources and Potential Exposure

People working for industries making or using benzene run the risk of being exposed to the highest level of benzene contamination. The general public is exposed to benzene from breathing emissions from burning coal and oil, fuel evaporations from gasoline service stations and exhaust of motor vehicles. Since it contains benzene, those exposed to tobacco smoke are also at risk for exposure to benzene. In fact, tobacco smoke accounts for nearly half of the American population’s exposure to benzene. Exposure can also occur by drinking water contaminated with benzene (see Environmental Protection Agency, 2007b).

Assessing Personal Exposure

According to the EPA (2007b), personal exposure to benzene can be measured in a person’s breath or blood. Breakdown products in a person’s urine (phenol) can also estimate the level of personal exposure. However, the tests must be performed close in time to the exposure. Furthermore, the tests are not useful in measuring low levels of benzene (see EPA, 2007b).
Benzene Exposure Limits

In its 11th Report on Carcinogens, the U.S. Department of Health and Human Services (2005) provided the following information from the Consumer Product Safety Commission (CPSC), Environmental Protection Agency (EPA), Occupational Safety and Health Administration (OSHA), Food and Drug Administration (FDA), the American Conference of Governmental Industrial Hygienists (ACGIH) and National Institute for Occupational Safety and Health (NIOSH) regarding some of the regulations and guidelines for asbestos exposure limits:

Regulations

CPSC

Products containing 5% or more by weight of benzene are considered hazardous and require special labeling Solvents for paints or other surface-coating materials containing 10% or more by weight of benzene require special packaging

EPA

Safe Drinking Water Act
Maximum Contaminant Level (MCL) = 0.005 mg/L

FDA

Maximum permissible level in bottled water = 0.005 mg/L
Residues of benzene used as a solvent in producing modified hop extract shall not exceed 1.0 ppm

In its 11th Report on Carcinogens, the U.S. Department of Health and Human Services (2005) stated that “benzene is known to bea human carcinogen based on sufficient evidence in humans” (p. 26). It is highlighted further in the Report that “the strongest epidemiological evidence that benzene causes cancer is from several cohort studies in various industries and geographical locations, which found that occupational exposure to benzene increased the risk of mortality from leukemia (mainly acute myelogenous leukemia) (U.S. Department of Health and Human Services, 2005, p. 26).

Acute effects. The co-exposure of ethanol (e.g., alcohol) with benzene increases the potential for benzene toxicity in humans. When humans are exposed to benzene through inhalation they can experience neurological symptoms such as drowsiness, dizziness, headaches and unconsciousness. When humans ingest large amounts of benzene they can have toxicity symptoms such as vomiting, dizziness and convulsions. Benzene in liquid and vapor form can irritate the skin, eyes and upper respiratory tract. Skin contact with benzene can produce redness and blisters (see Environmental Protection Agency, 2007b).

Chronic non-cancer effects. The chronic exposure to benzene through inhalation causes blood disorders in humans. Specifically, it affects bone marrow. Other blood related symptoms include aplastic anemia, excessive bleeding and immune system damage caused by changes in blood levels of antibodies and loss of white blood cells. It is reported that benzene can cause structural and numerical chromosomal aberrations when humans experience chronic exposure to it.

The EPA (2007b) provides the following information on risk levels associated with the chronic exposure to benzene:

The California Environmental Protection Agency (CalEPA) has established a chronic reference exposure level of 0.06 milligrams per cubic meter (0.06 mg/m3) for benzene based on hematological effects in humans. The CalEPA reference exposure level is a concentration at or below which adverse health effects are not likely to occur. It is not a direct estimator of risk, but rather a reference point to gauge the potential effects. At lifetime exposures increasingly greater than the reference exposure level, the potential for adverse health effects increases.

ATSDR has established an acute inhalation minimal risk level (MRL) of 0.2 mg/m3 (0.05 parts per million [ppm]) based on immunological effects in mice and an intermediate MRL of 0.01 mg/m3 (0.004 ppm) based on neurological effects in mice. The MRL is an estimate of the daily human exposure to a hazardous substance that is likely to be without appreciable risk of adverse noncancer health effects over a specified duration of exposure (Environmental Protection Agency, 2007, p. 2).

Reproductive/developmental effects. Occupational studies reveal that benzene has the potential to impair fertility in women under conditions of high exposure. The results of human studies are somewhat limited in that they did not have exposure history, a lack of follow-up and there was simultaneous exposure to other chemicals.

Cancer risk. Occupational exposure to benzene increases the incidence of leukemia. The EPA (2007b) provides the following information on the estimated risk for cancer due to exposure to benzene at certain levels:

EPA uses mathematical models, based on human and animal studies, to estimate the probability of a person developing cancer from breathing air containing a specified concentration of a chemical. EPA calculated a range of 2.2 x 10-6 to 7.8 x 10-6 as the increase in the lifetime risk of an individual who is continuously exposed to 1 µg/m3 of benzene in the air over their lifetime. EPA estimates that, if an individual were to continuously breathe air containing benzene at an average of 0.13 to 0.45 µg/m3 (1.3 x 10-4 to 4.5 x 10-4 mg/m3) over his or her entire lifetime, that person would theoretically have no more than a one-in-a-million increased chance of developing cancer as a direct result of continuously breathing air containing this chemical. Similarly, EPA estimates that continuously breathing air containing 1.3 to 4.5 µg/m3 (1.3 x 10-3 to 4.5 x 10-3 mg/m3) would result in not greater than a one-in-a-hundred thousand increased chance of developing cancer, and air containing 13 to 45 µg/m3 (1.3 x 10-2 to 4.5 x 10-2 mg/m3) would result in not greater than a one-in-ten thousand increased chance of developing cancer (Environmental Protection Agency, 2007b, pp. 2-3).

Conclusion

Asbestos and benzene are recognized as being carcinogenic to humans and permeate the environment in one way or another. The scientific data on their deleterious health effects is unambiguous, making them a serious health threat. Both chemicals have a long and varied history of industrial application in the United States. Their extensive industrial application makes them especially dangerous to the health of people, generally, and those people are exposed to them on a regular basis, specifically.

Asbestos and benzene are just two examples of toxic agents linked to cancer. As it was pointed out earlier, they are illustrative of the cancer-causing agents contaminating the environment. There are hundreds of other carcinogenic agents reported in the literature by numerous governmental and private health agencies. For example, the IARC’s (2008b) list contains 419 agents recognized to be to some greater or lesser statistical sense linked to cancer, while the Eleventh Report on Carcinogens (U.S. Department of Health and Human Services, 2005) lists 246 entries.

The point is that we just do not live in a benign toxic world. Instead, we live in a toxic world which poses serious health risks, cancer being one among them. Consequently, it would be prudent for anyone even casually interested in remaining healthy and living a long, vital life to become more informed about carcinogenic agents, which pose a serious health hazard to the extent that they can literally take one’s life. According to the American Cancer Society (2008), approximately 565,650 Americans are expected to die of cancer this year. That comes to more than 1,500 people a day. Cancer ranks as the second most common cause of death in the United States, accounting for one of every four deaths.

The earlier cited statistic that “80% of all cancers are directly or indirectly linked to environmental factors, and, thus, are preventable” (International Agency for Research on Cancer, 2008a, p. 1) underscores the importance of learning more about the toxic environment in which we live and how to protect our wellbeing and prevent cancer through the daily practice of proper nutrition and a healthy lifestyle.

The purpose of this month’s issue of Healthful Hints was to provide a sense of what scientists and others involved in the research effort to prevent and cure cancer know about causing-cancer agents pervading the environment and hopefully inspire readers to learn more about their toxic world, especially that part constituted of cancer-causing agents.

International Agency for Research on Cancer (n.d.). IARC monographs on the evaluation of carcinogenic risks to humans. Retrieved February 1, 2007b, http://monographs.iarc.fr/

National Institute for Occupational Safety and Health (1997). U.S. Department of Health and Human Services (1997) Asbestos bibliography (Revised). Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. Retrieved February, 1, 2007, from http://www.cdc.gov/niosh/pdfs/97-162.pdf.

U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program (2005). Report on Carcinogens, Eleventh Edition. Retrieved February 1, 2007 from http://ntp.niehs.nih.gov/ntp/roc/toc11.html